1. Field of the Invention
The present invention relates to a laser processing system including a laser optical path that guides laser beam emitted from a laser oscillator to an object to be processed.
2. Description of the Related Art
When such impure gases as to diffuse or absorb laser beam is present around a laser processing system, a large influence on a laser beam propagation property is generated. Accordingly, in a conventional laser processing system in which a laser oscillator is mounted, a laser optical path including an optical system that guides the laser beam from a beam emission port of the laser oscillator to a processing point is provided. Moreover, such a laser optical path is filled with a clean purge gas that fails to influence the laser beam propagation property, which allows laser processing to be stable.
Further, Japanese Patent Publication No. 4335154 discloses an invention of the conventional laser processing system as described above, in which a gas sensor for detecting impure gases is provided in the laser optical path to determine whether or not the impure gases were mixed in the laser optical path.
Meanwhile, in the conventional laser processing system as described above, in accordance with improved precision of laser processing and improved output, a purge gas that is to fill the laser optical path is diversified. For example, a dry air, an air in which carbon dioxide causing scattering of laser is reduced, nitrogen-rich gas (i.e., gas containing nitrogen as a main component), nitrogen gas or the like is used as the purge gas.
In particular, a special filter, such as a hollow fiber filter, an oil mist filter, an activated carbon filter or the like is used to generate a dry air or an air in which carbon dioxide is reduced. However, when a gas is allowed to permeate such a special filter, oxygen concentration in the purge gas increases or decreases. Then, the oxygen concentration in the laser optical path greatly changes with passage of time. At this time, even when the impure gases are not mixed in the laser optical path, the gas sensor reacts to a change of the oxygen concentration and an output value of the gas sensor also changes with passage of time. Consequently, when the gas in which the oxygen concentration is changed is used as the purge gas, it will be difficult to correctly determine whether or not the impure gases were mixed in the laser optical path.
In addition, when whether or not the impure gases were mixed in the laser optical path is determined, the output value of the gas sensor is compared with a predetermined determination threshold value. With respect to the determination threshold value, a certain allowance range is commonly set in consideration of an error of the output value of the gas sensor due to an environment. That is the reason why, as the environment in which the laser processing system is installed, such as a temperature, a humidity and an altitude, changes, the output value of the gas sensor relative to the same gas type also slightly changes. However, when the determination threshold value including the certain allowance range is thus set, determination of a mixing of the impure gases may contain an error if the output value of the gas sensor changes in accordance with the change of the oxygen concentration in the laser optical path. Thereby, the laser processing system may erroneously operate.